The present invention relates generally to machine tools, and more particularly, to a semi-automatic tool changing apparatus which is advantageously used with or incorporated in machine tools which receive cutters, bits, or the like in a collet type chuck.
At present, many small and medium size machine tools, such as milling machines, for example, removably receive milling cutters in a spindle which in turn receives a collet. The collet is adapted to snugly engage the tool by radial compression when the body of the collet is urged into a taper by the action of a so-called drawbar. The drawbar is essentially a long bolt having a threaded portion adapted for cooperative engagement with counterpart threads in the end of the collet opposite the tool-receiving collet end. The drawbar also has a shank portion and a head portion which is engaged by a wrench manipulated by the operator when it is desired to change tools. This is accomplished by locking the spindle against rotation, loosening the drawbar, permitting the collet to slide slightly out of the taper and release its hold on the tool. Thereupon, a new tool is placed in the collet and tightened by opposite hand manipulation of the drawbar, or a new collet and a tool associated therewith are placed in the tapered spindle opening and locked in place by engaging threaded portion of the collet with the threaded drawbar end, and securing the collet in the taper by rotating the drawbar until the collet is snug in the taper.
In machine tools such as a "Bridgeport" brand vertical mill, the drawbar extends through the entire length of the spindle and the spindle reciprocates within a carrier known as the quill. The spindle is driven by a direct or indirect gear arrangement, and a quill and the spindle carried thereby are moved generally downwardly to a work-engaging position and, in some cases, continue to move axially (downwardly) while the tool engages the work so as to complete a milling operation.
In other cases, the quill remains in a fixed position and the work is moved radially thereof on the table, for example.
In machining operations, in which the tools and its associated collet are changed frequently, a considerable amount of time is spent manipulating the parts just referred to for the simple purpose of tool changing. In some cases, it has been proposed to simplify the tool changing task by the use of accessories, or by the use of special collets or fixtures. Devices of this sort have not usually met with significant acceptance, for at least two principal reasons, as well as others of less importance.
The first of these is that, with a number of machine tool attachments, the effect of so-called quick changing head devices is to situate the tool a significantly extended distance from the bearings which journal the quill and/or the spindle. In other words, where the tool chucking device extends downwardly from the position normally occupied by the collet, the structure supporting the tool is subject to a substantial moment arm and lacks the stiffness which is present when the tool is located close to the collet. Accordingly, as the work is fed to the tool, the tool may deflect enough to interfere with the making of precision cuts. In addition, such a cutting arrangement, which lacks the requisite stiffness, may be subject to chatter in use and will otherwise perform less satisfactorily than where the tool is held in a more rigid arrangement.
A second disadvantage of prior art tool holders intended to permit convenient tool changing is that the devices tend to multiply any misalignment in the spindle and/or quill by reason of extending well past a surface supported by bearings. Such so-called quick change adaptors themselves lack flexibility and, if less than perfectly square, do not perform as satisfactorily in use as would be theortically anticipated. In other words, the static and dynamic radial runout of the tool itself, even when no load is present, is undesirably multiplied. As a consequence, quick change devices of this character, which are basically additional locking devices in series with the locking devices forming a part of the basic machine, have never enjoyed widespread acceptance.
Moreover, inasmuch as these so-called quick change adaptors use specifically designed collets, they require purchase in complete sets, including a master adaptor, and the cost of such quick change adaptor with an array of collets may cost from perhaps $300 up to $600 or more. Still further, devices of this sort still require manipulating a cap nut in order to change the tool.
According to the present invention, an arrangement is provided in which the vertical mill or other machine tool using a drawbar locking system is or may be operated in the normal manner in use, but is provided with a combination quill overtravel switch, motor, and impact driver type assembly for intermittently engaging the drawbar head and locking or unlocking it automatically. In a typical use of a machine modified to incorporate the features of the present invention, after the quill is in its normal, raised position, the quill feed is moved just slightly upwardly of such preset position, and this energizes a motor and causes engagement between the drawbar impact drive driven by the motor and the drawbar, thus loosening the collet or clamping it in place within the end of the spindle.
According to the invention, the milling machine or the like operates in the normal mode throughout its normal range of quill travel, and the motor driven locking and unlocking arrangement is merely added to the top of the turret. The quill feed is arranged to return to a rest position just short of its normal, fully raised position. When it is raised further against the pressure of a spring, switch contacts are engaged as long as the quill is so held, for locking or unlocking the tool.
In view of the foregoing drawbacks of known tool changing systems for machines using drawbar tool locking systems, it is an object of the present invention to provide an improved locking and release mechanism for a machine tool unit.
Another object is to provide an improved machine tool having semi-automatic tool changing capabilities.
Another object of the invention is to provide a modified machine tool which operates in its normal mode but which may also be simply manipulated so as to release and lock the tool holder in a semi-automatic manner.
Yet another object is to provide a motor driven attachment to a machine tool which is adapted to facilitate locking and unlocking tools and collet chucks used to secure the tools in place within the machine.
A still further object is to provide an arrangement of machine tool, motor, and drive unit for intermittent connection between the motor and the drawbar serving to lock a tool holder in place within the unit.
Another object is to provide a low cost, simple and straightforward semi-automatic tool changer for a machine tool.
A still further object is to provide a machine tool holder locking and unlocking arrangement capable of using readily available, low cost elements or parts for providing intermittent engagement between a motor for supplying rotational energy and the drawbar which locks the tools in place within the machine.
A further object is to provide a quick, semi-automatic tool changing arrangement which does not require making any changes to the operating mode of existing machine tools.
Still another object is to provide a semi-automatic tool changer which is adaptable to different forms of milling machines and the like and which may be added to existing machines without great expense or difficulty.
The foregoing and other objects and advantages of the invention are achieved in practice by providing a tool holder arrangement including a locking and unlocking motor, cooperating clutch means associated with the motor and the drawbar for forming an intermittent, torque-transmitting connection therebetween, means for moving the clutch means into and out of engagement under the control of an operator, and means for energizing the motor when the drawbar and the motor portion are operatively engaged so as to permit tightening, loosening or releasing a tool or tool holder held in position within an associated machine tool.
The manner in which the foregoing and other objects and advantages of the invention are achieved in practice will become more apparent when reference is made to the following detailed description of the preferred embodiments of the invention set forth by way of example and shown in the attached drawings with which like reference numerals indicate corresponding parts throughout.